Hundreds of police departments in two states were found to have broken laws mandating police reports for in-custody deaths. Registries required by California and Texas were missing a total of 660 deaths from 2005 to 2015.

They are the only two states that require law enforcement to report all in-custody deaths, but it seems enforcing the law is trickier than anyone imagined. Research from Texas State University in San Marco found that the two states did not report hundreds of deaths that involved officers during a 10-year period.

Texas was found to have failed to report 220 use-of-force fatalities, and California had 440 unreported deaths from 2005 to 2015, according to the Houston Chronicle.

Both Texas and California attorneys general confirmed that many hundreds of cases were missing. While failing to file such a report is a misdemeanor in Texas, there is no punishment for it in California.

“We’re not really blaming anyone – this is an incredibly complex problem,” Howard Williams, a professor who conducted the study, told the Houston Chronicle.

The study was conducted by Williams and Scott Bowman, with co-author Jordan Taylor. They found the missing reports by comparing the registries of reported fatalities to media reports and police press releases. Williams acknowledges there are a multitude of reasons for the discrepancies in reporting, but the lack of enforcement in California, he says, comes down to clerical errors.

“But it’s really hard for us to go back and change policy, improve training or purchase new equipment, when you simply lack the data to even know what’s going on,” he said.

California’s failure to report officer-involved deaths seems to have been a chronic problem in the state. Nicole Nishida, a Los Angeles County Sheriff’s Department spokeswoman, explained that her department’s failure to file required forms from 2006 to 2011 could be chalked up to a “clerical error” that was related to the form.

However, that does not cover four deaths that were unreported by the agency from 2013 to 2014.

“We are currently undertaking efforts to systematically update the data to the [California Department of Justice] following their reporting protocol,” she said in an email to the Chronicle.

In total, 180 police agencies in California failed to file reports on civilian deaths, and Texas had 139 agencies that did not file use-of-force or in-custody deaths.